Add APFPV mode switching

[henkwiedig]

This PR will add APFPV mode switching for SBC 2 beta 2 and greg's APFPV image.
Please remove/uncomment these lines in stream.sh:

# sudo systemctl is-active --quiet wifibroadcast || sudo systemctl restart wifibroadcast
# sudo systemctl is-active --quiet wifibroadcast@gs || sudo systemctl restart wifibroadcast@gs

apfpv-demo.mp4

[Lupinixx]

Build locally and tested it on my Runcam VRX. Works as expected, switched between APFPV and wfb-ng from the menu, did a flight with both.

[zhouruixi]

1. Should we store APFPV settings in the pp_rk configuration file instead of retrieving them from other software configurations via commands?

2. Would it be simpler and more flexible to use wpa_supplicant instead of networkmanager to manage connections?

[seriyps]

sorry, I created a conflict with my other PR. But I think a better way to resolve it would be to not start WFB thread at all in main() (force-set wfb_port to 0 or have a dedicated flag for it).

[seriyps]

UPD just realized that RXMODE can change at runtime...

[Lupinixx]

What is keeping this from merging // getting approved? If something still needs to be tested i am happy to help.

[henkwiedig]

Will merge here this weekend if no one vetos.

[zhouruixi]

The GS supports both WFB and AP modes, but the camera requires two different firmware versions, which is very strange. I still maintain that the camera should support both modes simultaneously. I wonder if Igor has changed his mind; perhaps this will be an important step towards promoting dual-mode support for cameras.

Additionally, I think using a GS as AP is better than using camera as AP. Multiple cameras can connect to one GS, and laptops can be on the same network as camera. GS can also more easily copy and forward traffic, etc.